The problems caused by ingestion of foreign objects into the air inlet of jet engines have long been recognized in the art. This problem is particularly acute with jet engines used on aircraft, since such engines are operated in an environment where foreign objects cannot be removed or controlled. The engines of jet aircraft taxiing on the ground frequently ingest foreign objects such as tools and other small metal objects, while a jet aircraft in flight is susceptible to ingestion of birds, leaves, paper, and other airborne debris.
The ingestion of almost any solid foreign object into the air inlet of a jet engine causes damage to the compressor stages, and possibly to other portions of the engine. This engine damage is immediately manifested by a partial or complete loss of available engine thrust, with consequent impairment of aircraft flying ability.
The problem of bird ingestion into jet engines is particularly acute during aircraft take-off, where an aircraft may fly through a flock of birds at precisely the time when maximum available thrust is required for a safe take-off. Since many commercial and private jet-powered aircraft have only two engines, it will be appreciated that a partial loss of power in both engines, or a total loss of power in one engine, occurring during or shortly after take-off can have drastic consequences. Post-crash investigations have proved that numerous jet aircraft crashes, resulting in loss of life and extensive property damage, are directly attributable to bird ingestion which occurred during or shortly after take-off.
According to FAA statistics, there have been over 100,000 (Civil and USAF) wildlife strikes between 1990 and 2008, and the number of strikes has climbed steadily since 1990. In 1990, the industry saw 1,738 bird strikes; in 2007, the number had increased to 7,666. Some of that trend is due to increased air travel, but the frequency of wildlife strikes has tripled from 0.527 to 1.751 per 10,000 flights.
Bird strikes, particularly of the jet's engines, can have catastrophic consequences. On Oct. 4, 1960, Eastern Air Lines Flight 375 was struck by a flock of European starlings during take-off. All four engines were damaged and the aircraft crashed in the Boston harbor. There were 62 fatalities.
Although FAA regulations require that jet engines be designed to permit continued operation after ingesting a bird of specified size at a specified aircraft speed, such design has not eliminated bird strikes causing engine damage and/or failure. On Jan. 15, 2009, a double bird strike involving Canadian geese impacted U.S. Airways Flight 1549, an Airbus A320-214, about three minutes after take-off from La Guardia airport, when the airplane was at an altitude of 2,818 feet AGL (above ground level). The bird strike resulted in an immediate and complete loss of thrust to both engines, forcing the crew to ditch the plane in the Hudson River.
FAA statistics report that 92% of bird strikes occur at or below 3,000 feet AGL, thus at a critical point of takeoff or landing. Proposed ground-based wildlife abatement programs, such as radar detection of bird flocks and use of lights, noise makers, and water cannons are of little to no use in abating bird strikes at altitudes such as Flight 1549 experienced, or higher altitudes.
The increase in bird strikes has resulted in regular reports of commercial jets being forced to make emergency landings shortly after takeoff. According to FAA statistics, gulls are the most common type of bird to strike aircraft, accounting for 19% of the birds identified in bird strikes. Doves and pigeons are the second most common, accounting for 15% of the birds identified in bird strikes. But as Flight 1549 proves, bird strikes of larger birds such as Canada geese can also occur, with devastating consequences.
There are many factors contributing to increasing rates of bird strikes by commercial and military aircraft. These factors include: 1) As jet travel replaced the noisier and slower piston-powered aircraft, the chance of these jets colliding with wildlife increased; 2) Along with the change in mode of travel there has been an increase in air traffic worldwide, both military and commercial; 3) Natural habitat surrounds many modem airports and this habitat provides shelter, nesting area, and feeding areas for wildlife that is not usually present in the surrounding metropolitan area; 4) Many of the world's busiest airports, including Washington Reagan National, Philadelphia International, New York La Guardia, and Boston Logan International, are near large bodies of water that create the aforementioned natural habitats for large water fowl such as geese and ducks; 5) Wildlife conservation measures generally serve to increase the populations of native birds. These factors result in a majority of wildlife strikes occurring within the immediate airport environment. According to FAA statistics, over $600 million dollars annually is lost due to wildlife strikes with civil aircraft in the United States alone.
The term “jet engine” as used herein is intended to include various types of engines which take in air at a relatively low velocity, heat the air through combustion, and expel the air at a much higher velocity. The term “jet engine” includes turbojet engines and turbofan engines, for example.
A jet engine conventionally comprises a compressor section for compression of the intake air, a combustion section for combustion of the compressed air and a turbine section arranged behind the combustion chamber, the turbine section being rotationally connected to the compressor section in order to drive this by means of the energy-rich gas from the combustion chamber. The compressor section usually comprises a low-pressure compressor and a high-pressure compressor. The turbine section usually comprises a low-pressure turbine and a high-pressure turbine. The high-pressure compressor is rotationally locked to the high-pressure turbine via a first shaft and the low-pressure compressor is rotationally locked to the low-pressure turbine via a second shaft.
In the aircraft jet engine, stationary guide vane assemblies are used to turn the flow from one angle to another. The stationary guide vane assembly may be applied in a stator component of a turbo-fan engine at a fan outlet, in a Turbine Exhaust Case (TEC) and in an Inter-Mediate Case (IMC).